1. Field of the Invention
The present invention pertains to an improved bicycle stem clamping structure for providing a cantilevered support for a handlebar, especially for mountain bikes or the like.
2. Discussion of the Prior Art
Bicycles include handlebars to apply directional control to a front fork and wheel, for steering the bicycle. A front fork includes a substantially vertical steering or steerer tube inserted coaxially within the head tube of the bicycle frame. A bicycle handlebar stem is usually supported within a fork steerer tube and retained therein by an offset expander wedge providing pressure applied by an expander bolt. The stem also normally includes a roughly horizontal, cantilevered support portion terminating in a transverse stem clip which, along with a binder bolt, can be used to clamp a substantially horizontal handlebar in place. The handlebar, as is well known in the art, is used to steer the bicycle; the stem, combining the horizontal cantilevered portion and the vertical portion within the steerer tube, provides one method for supporting the handlebar and applying pressure from the handlebar to the front fork for steering the bicycle. A number of attempts have been made to provide greater support for mountain bike handlebars which frequently endure greater stress in technical riding, competition or the like. In particular, the ball type handlebar, popular in the late eighties, incorporated the handlebar and stem into a one piece unit including an expander bolt and an expander wedge for clamping the handlebar and integral stem into the steerer tube. A number of problems were observed with the ball type handlebar, including a lack of adjustability.
Others trying to solve the problems inherent in mountain bike handlebar mounting and adjustment created the xe2x80x9cAheadset(trademark)xe2x80x9d bicycle stem including a steerer tube attachment, a substantially horizontal stem member, and a removable handlebar clamping member, thereby providing added flexibility in bike fit but incorporating a complicated and inherently weaker structure into a mechanism for mounting a handlebar to a mountain bike.
There is a need, therefore, to provide a strong, mechanically robust and yet simple structure for mounting a mountain bike handlebar onto steerer tube which permits easy adjustability.
Accordingly, it is a primary object of the present invention to overcome the above mentioned difficulties by providing a strong, mechanically robust and yet elegantly simple structure for mounting a mountain bike handlebar onto steerer tube while permitting convenient adjustment.
Another object of the present invention is to mount a handlebar onto a bicycle with an economically manufactured clamping structure.
Yet another object of the present invention is adjustably clamping a handlebar onto a bicycle in an aesthetically pleasing, rigid clamping structure made from a selected material, thereby allowing the user to select the structure and material best suited to their riding style and budget.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
In accordance with the present invention, a bicycle stem clamping structure is readily manufactured in two matching parts. A twisted bicycle stem includes first and second helically twisted clamping members fastened together using four threaded fasteners received in four corresponding threaded apertures. The assembled twisted stem defines, at one end, a vertical cylindrical receiving aperture opposite, at the other end, a transverse, substantially horizontal cylindrical receiving aperture having a central axis offset by 90xc2x0, or in perpendicular relation, with the central axis of vertical receiving aperture. The first and second helically twisted clamping members each comprise one-half of the finished stem structure for receiving the substantially horizontal handlebar and the substantially vertical steerer tube.
The first and second helically twisted clamping members are preferably manufactured of steel, aluminum, titanium, magnesium or thermoplastic or plastic engineering resin such as Grivory GV-5H(trademark) brand reinforced thermoplastic, preferably reinforced with a 50% glass fiber fill or carbon fiber fill using high tensile strength filaments.
Each of the helically twisted clamping members includes a twisted longitudinal external scoop or groove and functions as a twisted I-beam, thereby saving material and weight and providing a shape which permits the helically twisted clamping members to be cast or molded and removed from the mold with both mold and cast or molded clamping member intact. A plurality of identical helically twisted clamping members are preferably fabricated in a single mold and two members are used to fabricate a twisted bicycle stem. The transverse extent of the scoop is bounded by first and second opposing ribs, also helically twisted in a 90xc2x0 turn or quarter twist.
In an alternative embodiment, the helically twisted clamping member vertical receiving aperture and horizontal receiving aperture are defined by first and second sleeves fabricated from aluminum, titanium, thermoplastic or thermoset plastic. The first and second helically twisted clamping members have helically twisted inwardly facing surfaces which, in the assembled twisted bicycle stem, are in intimate contact with one another. In an alternative embodiment, an aluminum, titanium or steel sheet is incorporated into each helically twisted clamping member on the inwardly facing surface, thereby imparting additional strength to the finished twisted bicycle stem. In another alternative embodiment, each helically twisted clamping member has a pin or tab and corresponding symmetrically disposed hole or slot on an inwardly facing surface, where the hole is adapted to receive the pin on the mating helically twisted clamping member or the slot is adapted to receive the tab on the mating helically twisted clamping member, thereby assisting in aligning and indexing the first and second helically twisted clamping members and providing additional mechanical support to the resulting twisted bicycle stem structure.
The helically twisted clamping members may alternatively be machined from titanium, aluminum, steel or the like. Machined helically twisted members can be substantially hollow inside, thereby defining a cavity, once assembled into a finished twisted bicycle stem. For those embodiments having removable sleeves, the user has additional flexibility since the sleeves can be sized to receive different vertical stem tube and handlebar diameters. The length of each sleeve can be varied to provide greater adjustment in rise or stack height. The length between the vertical cylindrical receiving aperture and horizontal cylindrical receiving aperture (i.e., the distance between the central axes of the receiving apertures) can be varied to give a twisted bicycle stem of any desired stem extension (from steerer tube to handlebar). A steerer tube of any desired length and diameter can then be received in the vertical cylindrical receiving aperture and a handlebar of any desired diameter can be received in the horizontal cylindrical receiving aperture. Thus, helically twisted clamping members each comprise one-half of the finished stem structure for receiving the handlebar and the steerer tube. In the preferred embodiment, the helically twisted clamping members are substantially identical and are therefore more economical to manufacture than differing parts. Removal of threaded fasteners permits simultaneous removal of the stem and handlebar, thereby allowing rapid changes in equipment or ease of access to individual parts for ease of maintenance.
A machined, twisted bicycle stem is assembled using threaded fasteners received in threaded apertures and clamping a substantially horizontal handlebar that is separated by a stem extension distance from a substantially vertical steerer tube supported within a bicycle frame by a headset. The stem extension distance between the horizontal receiving aperture and the vertical receiving aperture are preferably in the range of 50 millimeters to 150 millimeters. Preferably, the threaded fasteners are metallic fastening bolts positioned in front and in back of the steerer tube and in front and in back of the handlebar, to provide a powerful clamping force on the steerer tube and on the handlebar when fastened to join the two helically twisted clamping members or halves together. The helical form and the incorporated reinforcing sleeves and gussets resist flexing movement under dynamic loading and provide a rigid and responsive ride to the bicyclist. Steering accuracy and control in demanding or highly technical riding situations are therefore enhanced. By providing two identical halves in the stem structure, quick and easy breakdown of the front of the bicycle are provided. This also permits easy breakdown for maintenance or for transport in limited space. Slotted sleeves or shims can be used to resist crimping of the handlebar and fork steerer tube by dissipating stress during dynamic loading. The fork steerer sleeve may be cut in different lengths for use in different stack height/steerer length configurations and is preferably cut to a selected length allowing for proper vertical tightening of the head set without exerting direct pressure on the two main halves of the stem.
Another embodiment of the stem of the present invention has a central body portion formed as a helically twisted solid central portion terminated at a proximal end in a first hinged clamping member adapted to clamp on and retain a substantially vertical steerer tube, and terminated in a distal end in a second hinged clamping member adapted to clamp on and retain a substantially horizontal handlebar. The first and second hinged clamping members are each releasably fastened to the solid central portion using one or more threaded fasteners.
The stem design of the present invention may be retrofitted to a threaded head set/steerer tube configuration by substituting an unslotted, hollow quill with an expanding wedge and tightening bolt for the fork steerer sleeve used in threadless headset/steerer applications. Fastening of the two helically twisted clamping member halves will be identical for both types of assemblies, however, tightening the stem wedge bolt is necessary for a secure fitting with threaded headset/steerer configurations.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components.